Process for controlling and/or guiding the weld seam during arc welding and a paint therefor

ABSTRACT

A process for the control and/or guidance of welds in electric arc welding wherein a metal or a metal alloy is applied to the edge or surface to be welded of at least one workpiece, with the metal or at least one of the principal alloying metals not being present in the workpiece or at least in slight proportions only, so that a characteristic spectral line emitted by at least one of the metals applied is observed spectroanalytically in the arc and that the weld is controlled and/or the arc guided by means of the spectral data determined.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a process for the control and/or guidance ofwelds in arc welding and a lacquer to be used in the process.

2. Description of the Prior Art

In order to enhance productivity, save energy and raw materials and toimprove the quality of products, attempts are always made to carry outand to control manufacturing processes automatically.

The principal problem of arc welding technology consists of the need toguide the welding arc automatically along the weld joint. This, however,requires the availability of appropriate sensor systems capable ofsecurely following the weld joint in order to automatically assure thepositioning of the welding burner in its path following the existingweld joint.

Different sensor systems have already been proposed. A review may befound in the article by P. Drews and G. Starke, "Sensors in Weldingtechnology", Umschau 1985, No. 5, page 296.

In the arc welding of safety parts there exists the further need tocontrol the quality of the weld.

The sensor systems used at the present time for the guidance of the arcand to control quality, are technically involved and thus veryexpensive. In the case of certain parts, such as for example deepdrawing sheets, these known sensor systems cannot be used at all.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a welding processmaking possible the simple guidance of the weld or the burner,respectively, and/or the control of the weld during electric arcwelding. A coating agent, in particular a lacquer capable of being usedin such a process, is to be provided further.

The object of the invention is thus a process characterized in that ametal or a metal alloy is applied to the edge of a surface to be weldedof at least one workpiece, with the metal or at least one of theprincipal alloying metals, not being present in the workpiece or only insmall proportions, in that at least one characteristic spectral line inthe arc emitted by at least one metal applied to the workpiece isobserved spectroanalytically, and that by means of the spectral dataobtained the weld is controlled and/or the arc guided.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE of the drawing schematically depicts an apparatus forpracticing the invention.

DETAILED DESCRIPTION OF THE INVENTION

Due to the high temperature of the arc, not only part of the metalspresent in the material and the weld wire is evaporating, but also apart of the metals applied. Simultaneously, the evaporated metals areexcited by the arc and emit a spectrum characteristic of them. The arcthus serves as a spectroanalytical light source.

The emission spectrum emitted by the individual metals is known. In theprocess according to the invention the light of the arc isspectroanalytically decomposed. The characteristic spectral line emittedby the metal applied (which for example is present in the elemental formor as an alloy) is measured. Thus for example the intensity of thisspectral line is determined.

The apparatus to carry out such an emission spectral analysis and todetermine the intensity of the spectral line is known to those skilledin the art and is described for example in "Fundamentals and methods ofchemical emission spectral analysis" by R. Mannkopff and G. Friede,Verlag Chemie, D 6940 Weinheim, 1975. The spectral lines characteristicof each of the metals are also listed in this work.

In order to be able to observe the arc from a close proximity, inparticular an optical device transmitting the rays by means of glassfibers is used. This optical device may be protected by non-interferingand constantly varying adapters, for example in the form of rolled foil(day light projector principle) or deflecting mirrors.

In the process according to the invention therefore for example theintensity of a characteristic spectral line of an applied metal isdetermined. This metal should preferably not be present in the workpieceto be welded or in the wire electrode of the burner or only in slightproportions. It has been found favorable to have the applied metalpresent in proportions lower than 5% and in particular 1%.

The metal may be applied to the workpiece to be welded by flame sprayingor plasma spraying. The arc-spray method is for example one of theseprocesses.

The metal may further be applied in the form of a powder. This powdermay consist of a metal in the elemental form or a metal alloy. It shallbe referred in the following discussion as metal powder. The processaccording to the invention will become more apparent below from thedescription of the use of such a metal powder.

As set forth above, the metal powder is applied to the edge or surfaceof at least one workpiece to be welded. If the burner in the course ofwelding deviates from the center of the weld, the intensity of thecharacteristic spectral line varies. If the burner deviates for examplefrom the center of the weld toward the workpiece to which the metalpowder has been applied, the quantity of the metal evaporated increasesand a higher intensity of the spectral line measured is observed.

If the arc on the other hand leaves the predetermined joint line in thedirection of the workpiece to which no metal powder has been applied,the amount of the metal evaporated from the metal powder applied,decreases. The intensity of the spectral line measured thereforedecreases.

By means of the data determined in this manner, the arc may then becontrolled with the aid of a computer and the burner guided in thecenter of the predetermined joint.

If the metal powder is applied to the edge on one workpiece only, thepreferred mode of operation is to compare the intensity of the emittedspectral line of the metal examined with a given intensity by means of acomputer and to regulate the welding burner accordingly.

In this manner, information may be obtained additionally relative to thequality of the weld. A nonuniform guidance of the weld thus is indicatedby a variation of the observed or measured spectral lines. From thevariation of the predetermined intensities of the spectral linesobserved, information may therefore be obtained concerning the qualityof the weld. Consequently, variations in intensity are indications ofthe homogeneous composition of the weld bath and the weld itself.

If the metal powder consists of a single metal, a metal is used thatunder normal conditions is stable in the elemental form. In the process,either in the elemental form or in the form of an alloy, metals are usedwhich do not interfere with the welding process and do not have adetrimental effect on the quality of the weld. The following metals areused preferably: Fe, Mn, V, Cu, Ti, Co, Nb, Ni, Mo, W, Cr, Zr, Ta, Hf,Ir, Os, Re, Ru, Rh, Al, Be, Ce, Ge, Au, La, Pd, Pt, Sc, Ag and U.Particularly preferred are the following metals: Fe, Mn, V, Cu, Ti, Co,Nb, Ni, Mo, W, Cr, Zr, Ta, Hf and Be.

A metal powder with a grain size of 0.1 to 500 μm, in particular from 1to 150 μm, is applied preferably, with the maximum of the grain sizedistribution being located between 1 and 80 μm.

The metal powder used may consist of a single metal or a metal alloy. Inthe latter case not merely the characteristic spectral line of one metalbut of several metals, may be used for the intensity measurement.

In a preferred form of embodiment of the process according to theinvention, a metal powder is applied to the edges or surfaces of all ofthe workpieces to be welded. Therefore, if two workpieces are to bewelded together, a metal powder is applied to both surfaces or edges.

However, these metal powders have different compositions. Thus, themetal powder applied to one surface contains at least one metal that isnot present in the metal powder applied to the other surface.

In this case again a metal powder may be used which consists either of ametal or a metal alloy. Mixtures of two or more metal powders may alsobe applied.

The welding of two workpieces may be carried out for example as follows.Two different metal powders, each consisting of a single metal, are usedand one of the powders is applied to one workpiece and the other metalpowder to the other workpiece. In the course of the welding theintensity of a spectral line of both metals is measured and the burneris guided in a manner such that both spectral lines are as intensive aspossible.

In this fashion a guidance of the weld burner in the center of the jointis obtained. If said burner deviates from the center of the joint, theintensity of one of the spectral lines will increase, while theintensity of the other one decreases.

It is obviously also possible to compare the measured intensity of thespectral lines with a predetermined intensity and to control the arc bymeans of this data. It is further possible to use the data accumulatedmerely for quality control. The arc may also be controlled in a mannersuch that upon a deviation of the measured intensity from the givenintensity the burner is stopped.

In this preferred form of embodiment metal alloys may again be used.Preferably, these alloys consist of metals which are not present in themetal alloy applied to the other workpiece or only in such slightproportions that the intensity of the corresponding spectral line isvery low.

The type of metals, the grain size and the grain size distribution areas stated above. It should be noted in this context that metals whichburn in the pure form and/or in a fine distribution, or are oxidized bycontact with air, are used in the form of an alloy in order to avoid theabovementioned phenomena. This is true for example for zirconium,titanium and vanadium.

Advantageously, the metal powder is applied to the edge or surface to bewelded as uniformly as possible.

It is possible for example to provide the workpieces to be welded withan adhesive coating and to apply the metal powder to it.

To insure the most uniform application possible of the metal powder, thelatter is preferably mixed into a coating or adhesive medium, inparticular a lacquer. This lacquer is then applied to the surface oredge to be welded.

Another object of the invention is therefore a coating medium, inparticular a lacquer consisting of a binder and optionally a solvent,containing the metal powder.

As the binder, substances are chosen which evaporate without residue inthe arc. These include for example polyvinylbutyral, PUR, EPO, alkyd andacryl binders. They may be physically drying resins, such aspolyvinylbutyral and polyacrylate resins, and two-component masses ofepoxy, polyurethane and acryl resins hardenable by means of a hardener.

The metal powder has preferably a grain size of 0.1 to 500 μm, inparticular 1 to 150 μm, with the maximum of the grain size distributionbeing between 1 and 80 μm. A grain size of 1 to 70 μm is especiallypreferred.

The metal powder preferably amounts to 5 to 90% by weight and inparticular to 25 to 50% by weight.

The lacquer preferably contains additives preventing the settling ofmetal particles and assuring a homogeneous distribution of the metalparticles, thereby introducing run-off stability. These additivesinclude in particular finely distributed aluminum and magnesiumsilicates, silica, soy lecithins, metallic soaps and silicone oils,higher polycarboxylic acids and polycarbonates. Thus for example, finelydistributed silica marketed under the designation of Aerosil, may beused.

Any conventional solvent compatible with the binder or binder-hardenercombination, may be employed. Thus for example xylene,methylglycolacetate and butylacetate may be used, together with theirmixtures.

A colorant may further be added to the lacquer. Thus it is advantageousfor example to color the lacquer differently according to the metalpowder employed, thereby indicating the type of metal powder present inthe lacquer.

A lacquer composition according to the invention consists for exampleof:

5-90% by weight metal powder

5-40% by weight resin (binder and hardener)

0-5% by weight additives, in particular inorganic fillers

0-1% by weight colorants

0-50% solvents.

The lacquer is applied as uniformly as possible to the surfaces andedges to be welded in order to obtain a defined thickness of the layer.The lacquer may be applied by immersion, spraying, rolling, etc.

A further object of the invention is thus the use of one of theaforedescribed lacquer compositions in a process for the guidance and/orcontrol of the weld in electric arc welding.

The process of the invention may be employed not only to guide the weld,but also to control the welded joint. If it is found for example thatthe intensity of a spectral line measured is becoming too high or toolow in the course of welding, the corresponding data may be stored forexample in an EDV (electronic data processing) installation. Thelocation involved may be corrected by rechecking and possibly rewelding,immediately or later.

The data obtained by the process according to the invention thus makespossible an indirect quality control of the weld.

The process of the invention may further be combined with other knownsensor systems for the positioning and guidance of the weld.

To ascertain whether the metal powders contained in a lacquer areactually built into the weld, the weld of an uncoated specimen and ofseveral specimens coated on both sides with different lacquers wereexamined by means of emission spectroanalysis.

The workpieces welded consisted of iron sheets according to DINstandards. The weld wire consisted of Mn, Fe and Si and was encased in athin copper sheathing. The electrode was made of tungsten.

The weld of the uncoated specimen contained metals in the followingproportions: Co=0.4%; Ti=0.05%; Nb=0.001%; Cu=0.24%; Zr=0.001%; W=0.001%and Mo=0.003%; rest Fe.

The following metal powders were employed in the case of the specimenscoated with differently doped lacquers:

    ______________________________________                                        Specimen 1:      titanium powder and cobalt powder                            2:               cobalt powder and niobium powder                             3:               titanium powder and niobium powder                           4:               tungsten powder and metal powder of an                                        alloy consisting of copper and zirconium                     5:               a mixture of tungsten/vanadium powder                                         and niobium powder.                                          ______________________________________                                    

Analysis of the coated specimens showed that the weld contained theabovementioned metals in the following proportions:

    ______________________________________                                        Specimen 1:     Ti = 0.30%; Co = 0.59%;                                       2:              Co = 0.30%; Nb = 1.41%                                        3:              Ti = 0.15%; Nb = 0.72%                                        4:              W = 0.33%; Cu = 0.47% and                                                     Zr = 0.82%                                                    5:              W = 0.31%, V = 0.11% and Nb = 0.56%.                          ______________________________________                                    

These results show that the metals applied in the form of metal powderswere incorporated in the weld.

Certain examples of the lacquer compositions that may be employedaccording to the invention are described below.

EXAMPLE 1

Lacquer with the following composition:

    ______________________________________                                        titanium powder with a grain size of 150 μm                                                        28.0% by weight                                       solvent mixture of xylene, methylglycol acetate                                                       50% by weight                                         and butyl acetate                                                             polyvinylbutyral        16% by weight                                         Aerosil                 5% by weight                                          Neo-Zapon orange (Zapon dye of BASF)                                                                  1% by weight                                          Detection and control: spectral line Ti:                                      489.173 nm                                                                    ______________________________________                                    

EXAMPLE 2

Lacquer with the following composition:

    ______________________________________                                        niobium powder (grain size 10 μm)                                                                 50% by weight                                          polybutylacrylate      14% by weight                                          solvent mixture of butylacetate and                                                                  31% by weight                                          methylisobutyltetone                                                          Aerosil                4.5% by weight                                         Zapon genuine-green    0.5% by weight                                         ______________________________________                                    

In these examples metal powders of cobalt, molybdenum, tungsten,chromium, nickel and of a (65%:35%) copper-zirconium alloy may also beused.

EXAMPLE 3

Lacquer with the following composition:

    ______________________________________                                        molybdenum powder (grain size 10 μm)                                                               20% by weight                                         polymethylmethacrylate  10% by weight                                         Thixatrol ST            1.5% by weight                                        butylacetal             20% by weight                                         xylene                  1.5% by weight                                        polycarbonate           0.5% by weight                                        dye (Zapon)             0.5% by weight                                        propylacetate           10% by weight                                         ethylglycol             36% by weight                                         Detection and control: spectral line Mo:                                      379.825 nm                                                                    ______________________________________                                    

EXAMPLE 4

Lacquer with the following composition:

    ______________________________________                                        nickel powder, Inco Type 255                                                                       45%                                                      Desmophen 55oU Bayer AG                                                                            10%                                                      Aerosil               3%                                                      silicone oil          2%                                                      butylacetal          30%                                                      methylisobutylketone 9.5%                                                     dibutyltin-dilaurate 0.5%                                                     ______________________________________                                    

Hardening was effected with Desmodur N 3200 (Bauer AG) in astoichiometric proportion (but hardening may also be effected by under-or over-cross-linking).

EXAMPLE 5

Lacquer having the following composition:

    ______________________________________                                        tungsten powder, grain size 1 μm                                                                       30%                                               vanadium, grain size 20 μm                                                                             10%                                               (the vanadium powder was processed under a pro-                               tective argon atmosphere)                                                     polymethylmethacrylate      15%                                               nitrocellulose              5%                                                Aerosil                     3%                                                ethylglycol                 15%                                               butylacetate                22%                                               Detection and control: spectral line                                          W: 430.21 nm                                                                  V: 437.924 nm                                                                 ______________________________________                                    

In the abovedescribed examples in particular metal powders of cobalt,chromium and a copper-zirconium (65%:35%) alloy may also be used.

In this example, the lacquer also serves to protect the vanadium powder.

With reference to the drawing, there is shown an apparatus forpracticing the invention as described herein. The apparatus includes aburner 1 disposed above a workpiece 2 and a workpiece 4 to which a weld3 is applied therebetween. An optical device 5 observes the arc producedby burner 1 and transmits the rays through an optical glass fiber 6 toan apparatus 7 which provides an emission spectral analysis of theemitted spectrum. The spectral data obtained from apparatus 7 is used tocontrol and/or guide the welding arc.

We claim:
 1. A process for controlling, guiding or controlling andguiding the production of a weld seam during the electric arc welding ofworkpieces, which process comprises the steps of:(a) applying anelemental metal or an elemental metal alloy to an edge or surface of atleast one workpiece, wherein the elemental metal or at least one of themetals of the elemental alloy is either not present or present in slightproportions only in the workpiece; (b) applying a welding arc to theworkpiece provided with the elemental metal or elemental metal alloyapplied thereto; (c) spectroanalytically observing at least onecharacteristic spectral line in the arc emitted by at least one metal ofthe applied elemental metal or elemental metal alloy and derivingspectral data therefrom; and (d) controlling, guiding or controlling andguiding the arc in response to the spectral data so derived.
 2. Theprocess of claim 1 wherein two workpieces are welded together, andfurther including the steps of:(a) applying a first elemental metal oran elemental metal alloy to a surface or edge of one workpiece; (b)applying a second elemental metal or metal alloy to a surface or edge ofthe other workpiece, wherein the second elemental metal alloy containsat least one elemental alloy metal not present in the first elementalmetal alloy; and (c) spectroanalytically observing a characteristicspectral line of the elemental metal or elemental alloying metal appliedto the other surface or edge.
 3. The process of claim 1 wherein theelemental metal or the elemental alloy includes a metal selected fromthe group consisting of Fe, Mn, V, Cu, Ti, Co, Nb, Ni, Mo, W, Cr, Zr,Ta, Hf, Ir, Os, Re, Ru, Rh, Al, Be, Ce, Ge, Au, La, Pd, Pt, Sc, Ag, Uand alloys thereof.
 4. The process of claim 3 wherein the elementalmetal or elemental metal alloy includes a metal selected from the groupconsisting of Mn, V, Cu, Co, Ni, Nb, Cr, Mo, Be, W and alloys thereof.5. The process of claim 1 further including the step of applying theelemental metal or the elemental metal alloy in powder form.
 6. Theprocess of claim 5 wherein the powder is of a grain size within therange of 0.1 to 500 μm, with a maximum grain size distribution beingbetween 1 and 80 μm.
 7. The process of claim 6 wherein the powder has agrain size of from 1 to 150 μm.
 8. The process of claim 1 furtherincluding applying the elemental metal or the elemental metal alloy inpowder form in a coating medium.
 9. The process of claim 8 wherein thecoating medium includes a lacquer.
 10. The process of claim 9 whereinthe lacquer comprises a binder, a solvent and an elemental metal or anelemental metal alloy.
 11. The process of claim 10 wherein the elementalmetal or elemental metal alloy includes an element selected from thegroup consisting of Fe, Mn, V, Cu, Ti, Co, Nb, Ni, Mo, W, Cr, Zr, Ta,Hf, Ir, Os, Re, Ru, Rh, Al, Be, Ce, Ge, Au, La, Pd, Pt, Sc, Ag, U andalloys thereof.
 12. The process of claim 11 wherein the elemental metalor elemental metal alloy includes a metal selected from the groupconsisting of Mn, V, Cu, Co, Ni, Nb, Cr, Mo, Be, W and alloys thereof.13. The process of claim 10 wherein the elemental metal or elementalmetal alloy is in powder form and further including an additive toprevent settling of the powder and maintaining a homogeneousdistribution of the powder, the additive including an element selectedfrom the group consisting of finely distributed aluminum silicate,finely distributed magnesium silicate, silica, waxes, soy lecithins,metallic soaps, silicone oils, polycarbonates and mixtures thereof. 14.The process of claim 10 wherein the elemental or elemental metal alloyis present in an amount of 5 to 90% by weight.
 15. The process of claim14 wherein the elemental metal or elemental metal alloy is present in anamount of from 25 to 50% by weight.